The invention relates to a band-gap reference circuit for generating a reference voltage with a specific temperature coefficient, the circuit comprising a first semiconductor element having at least one junction for generating a junction voltage with a negative temperature coefficient, which first semiconductor element is coupled between a first and a second supply voltage terminal, a current source for generating a reference current with a positive temperature coefficient, which current source is coupled between the second supply voltage terminal and an output terminal, and a resistive element for carrying at least a measure of the reference current, which resistive element is coupled between the output terminal and the first supply voltage terminal.
Such a band-gap reference circuit can be used in general for the generation of a reference voltage in integrated semiconductor circuits, the reference voltage being available for example between the output terminal and the first supply voltage terminal.
Such a band-gap reference circuit is known from FIG. 4.1 of the dissertation entitled "Integrated Circuits and Components for Band Gap References and Temperature Transducers", written by G. C. M. Meijer and published on Mar. 19, 1982 at Delft (Netherlands). The known band-gap reference circuit comprises the first semiconductor element constructed by means of a first transistor, the resistive element constructed by means of a resistor, and the current source constructed by means of a second transistor, the first transistor being coupled as a diode, and the first transistor, the resistor and the second resistor being coupled in series between the first and the second supply voltage terminal. In the band-gap reference circuit which is constructed and coupled in this way the junction voltage generated across the junction of the first semiconductor element corresponds to a base-emitter voltage generated by the first transistor, and the reference current generated by the current source corresponds to a main current in the second transistor, the base-emitter voltage having the negative temperature coefficient and the main current having the positive temperature coefficient. Since the first transistor, the resistor and the second transistor are coupled in series at least a measure of the main current with the positive temperature coefficient in the second transistor flows both through the first transistor and the resistor. In spite of this, the base-emitter voltage of the first transistor retains a negative temperature coefficient, while the resistor receives a compensation voltage with a positive temperature coefficient, the reference voltage generated by the band-gap reference circuit between the output terminal and the first supply voltage terminal being equal to the sum of the base-emitter voltage and the compensation voltage. As a result of this, the temperature coefficient of the reference voltage is determined by the negative temperature coefficient of the base-emitter voltage and the positive temperature coefficient of the compensation voltage, which temperature coefficients depend upon parameters and the dimensioning of the band-gap reference circuit.
A disadvantage of the known band-gap reference circuit is the supply voltage which it requires. For example, if a reference voltage with a temperature coefficient of substantially zero volts per temperature unit is desired the sum of the base-emitter voltage and the compensation voltage is dictated mainly by a band-gap voltage contained in the base-emitter voltage, which band-gap voltage is a physical constant and is 1.205 V in the case of silicon. Consequently, in the afore-mentioned case the required supply voltage, i.e. at least one saturation voltage as a result of the second transistor plus the sum of the compensation voltage and the base-emitter voltage, is larger than the voltage supplied by a standard button cell (1.2 V), which prohibits the use of the band-gap reference circuit in some circuit arrangements requiring a comparatively low supply voltage, such as for example hearing-aid circuits.